As the use of computers and networks has increased, so too has the desire to restrict access to resources so that they can be accessed by only the appropriate users. Each user typically has his or her own user credentials that he or she can provide in order to prove his or her identity and to indicate whether he or she is entitled to access a particular resource. Access to the particular resource is then permitted or denied based on the user's identity. However, such reliance on a user's credentials is not without its problems. One such problem is that this use of user's credentials constrains designers on how they can restrict access to particular resources. This can lead to more rigid access control systems, and frustration on the part of both designers and users of computers.